Photocouplers (including photorelays) convert an input electrical signal into an optical signal by using a light emitting element; and an electrical signal can be output by a light receiving element after receiving the optical signal. Therefore, the photocoupler can transmit the electrical signal in a state in which the input and output are insulated from each other.
In industrial equipment, office equipment, and household appliances, different power supply systems such as a DC voltage system, an AC power supply system, a telephone line system, a control system, etc., are disposed inside one device. However, operation errors may occur in the case where different power supply systems and circuit systems are directly coupled.
In such a case, normal operations can be maintained by using a photocoupler because the different power supplies are insulated from each other.
For example, many photocouplers are used in an inverter air conditioner or the like for a load that may be an alternating current load. In the case where photocouplers are used for signal switching in an integrated circuit tester application, an extremely large number of photocouplers are mounted; and it is extremely desirable to reduce the photocoupler size due to the need to reduce the mounting surface area on the substrate.